There are two basic techniques used in digital-to-analog converters (DACs). These are the sigma-delta (.SIGMA.-.DELTA.) such as used herein and the resistive or capacitive divider techniques.
The .SIGMA.-.DELTA. technique is attractive because it achieves high resolution by precise timing instead of precisely matched on-chip components (resistors). In addition, the expertise needed to produce thin film, laser trimmed analog components is difficult to obtain; whereas, high speed digital switching capability is commonplace in the semiconductor industry.
A basic .SIGMA.-.DELTA. DAC receives a digital signal which is summed with the inverse feedback of the analog output signal (after being reconverted to a digital signal) to provide an error signal. The error signal is then processed through an integrator and a comparator to provide the analog output signal. The analog signal is also processed through an analog-to-digital converter (ADC) to provide the feedback signal.